On Saturday, in the aftermath of a visit to Pyongyang by Secretary of State Mike Pompeo, a North Korean statement called the US stance on negotiations.

It is not yet clear whether Pompeo will meet with North Korea's leader Kim Jong Un before departing Pyongyang for Tokyo where he is expected to brief his Japanese and South Korean counterparts.

She stressed that USA policy hasn't changed, but did not explain why they're not using the phrase "complete, verifiable and irreversible denuclearization" - a phrase Pompeo himself used leading up to the historic summit between Kim Jong Un and Trump in Singapore on June 12.

But while Pompeo on Saturday painted a positive picture of the follow-up talks, North Korean officials accused the U.S. of trying to unilaterally pressure their country into abandoning its nuclear programme.

"The U.S. side came up only with its unilateral and gangster-like demand for denuclearization", a North Korean foreign ministry spokesman said in a statement carried by the official KCNA news agency.

'However, the attitude and stance the United States showed in the first high-level meeting (between the countries) was no doubt regrettable, ' the spokesman said. "Our expectations and hopes were so naive it could be called foolish".

In practical terms, Pompeo mentioned only that officials from both sides would meet on July 12 as a working group to discuss the repatriation of the remains of some USA soldiers killed during the 1950-1953 Korean War.

He also said that working level talks will begin soon on the destruction of a missile-engine testing facility.

"We talked about what the North Koreans are continuing to do and how it's the case that we can get our arms around achieving what Chairman Kim and President Trump both agreed to, which is the complete denuclearisation of North Korea", Mr. Pompeo said.

Following the agreement signed at the Singapore summit, it appears that again North Korea and the USA have only committed to broad strokes and say that now the hard work is beginning, NPR's Seoul correspondent Elise Hu tells Weekend Edition Saturday.

"These are complicated issues, but we made progress on nearly all the central issues", he said, according to pool reports from journalists who traveled with the secretary.

Both men said they needed to "clarify" certain elements of their previous discussions, but provided no detail.

In an exchange in front of reporters before the meeting, Kim asked Pompeo if he had slept well and the U.S. Secretary said he had. "So thinking about those discussions you might have not slept well last night".

"Particularly, they have suggested that they are disappointed by the United States insistence on focusing on the denuclearisation plans over what they described as big-picture issues", she said.

The trip was Mr Pompeo's third to Pyongyang since April and his first since the summit.

"Chairman Kim is. still committed" to that goal, Pompeo said, and he reiterated that Trump was "committed to a brighter future for North Korea".

Many analysts in the U.S foreign policy community, particularly nuclear disarmament experts, had cautioned that Trump was rushing into the talks with North Korea based on undue optimism against an obdurate country which was primarily seeking status recognition from the U.S and had no intention of denuclearizing unilaterally.

Pompeo and Kim met for almost three hours Friday and then had dinner amid growing skepticism over how serious Kim Jong Un is about giving up his nuclear arsenal and translating the upbeat rhetoric following his June 12 summit with Trump into concrete action.

A state department spokesperson said Mr Pompeo had been "very firm" in focusing on denuclearisation, as well as on security assurances and another important U.S. demand - the return of remains of USA service personnel from the Korean War. North Korea committed at the summit to the "immediate repatriation" of remains already identified, but that hasn't happened yet.